Prosthesis with resorbable collar

ABSTRACT

An articulating hemiarthroplasty prosthesis ( 10 ) for use in arthroplasty is provided. The prosthesis includes a stem ( 12 ) for implantation at least partially within the medullary canal ( 14 ) of a long bone ( 16 ) and a collar ( 20 ). The collar ( 20 ) is operably associated with the stem ( 12 ) and extends outwardly therefrom. At least a portion of the collar ( 20 ) includes a resorbable material. The prosthesis includes a head ( 30 ) and a cup ( 46 ) for engagement with the head ( 30 ).

CROSS REFERENCE TO U.S. PROVISIONAL PATENT APPLICATION

This Application is a Utility Application based upon U.S. ProvisionalPatent Application Ser. No. 60/302,113 filed Jun. 30, 2001, entitledPROSTHESIS WITH RESORBABLE COLLAR.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to the field of orthopaedics,and more particularly, to an implant for use in arthroplasty.

BACKGROUND OF THE INVENTION

This invention relates to implantable articles and methods formanufacturing such articles. More particularly, the invention relates tobone prosthesis and process for manufacturing the same.

There are known to exist many designs for and methods for manufacturingimplantable articles, such as bone prostheses. Such bone prosthesesinclude components of artificial joints, such as elbows, hips, knees andshoulders. An important consideration in the design and manufacture ofvirtually any implantable bone prosthesis is that the bone prosthesishas adequate fixation when implanted within the body.

Early designs of implantable articles have relied upon the use ofcements such as polymethylmethacrylate (PMMA) to anchor the implant. Theuse of such cements can have some advantages, such as providing afixation that does not develop free play or does not lead to erosion ofthe joining faces postoperatively. Maintaining a load or force at thecement bone interface assists in providing for good fixation and toprevent motion.

To assist in maintaining the load at the cement bone interface tapered,some highly polished stems have been designed without a proximal collarto permit the subsidence within the cement mantle. The stems are thuspermitted to move distally with respect to the resected bone. Long termcontrolled subsidence within the cement mantle minimizes cementabrasion.

Without a collar, however, the surgeon is intra-operatively challengedto position these stems both axially and rotationally. A less than idealposition of the stem within the bone, also known as malposition, hasbeen shown to limit the patients range of motion by inducing improperleg length, inadequate lateral stem offset or non-anatomical version ofthe stem.

Inadequate pressurization of the cement within the femoral canal hasalso been documented as a potential cause of improper cement technique.Centralization of the stem within the cement mantle is also critical forsuccessful results. Non-uniform or excessively thin cement/stem/boneinterfaces may lead to high internal stresses and subsequent cracks.Cement debris generation due to abrasion has also been shown to produceexcessive third-body wear of the polyethylene acetabular components aswell as potentially induce osteolytic reactions and bone resorptionsthat may lead to stem loosening. One single femoral stem that can singlyaddress these critical issues is the intended solution.

The proper distribution of stresses within the prosthesis and throughoutthe surrounding bone is a problem in the use of known hip joint systems.If too little stress is applied to the bone, resorption can occurleading to atrophy of the affected area. Too much stress may result inan undesirable hypertrophy of the affected area. In some prior art,femoral stem designs' excess forces are transmitted through therelatively rigid stem to the distal portion, resulting in hypertrophy ofthe bone surrounding the distal portion, and atrophy of the bonesurrounding the proximal portion of the stem.

Attempts have been made to provide for a proper amount of stress on thecement mantle of prosthesis. For example, in U.S. Pat. Nos. 5,171,275and 5,290,318 both to Ling, et al, incorporated herein by reference,disclose a tapered, collarless femoral hip joint prosthesis formed ofcobalt chromium-molybdenum alloy with a highly polished surface. Thestem is tapered in the anterior/posterior and medial/lateral directionsand has rounded corners.

The tapered collarless design permits the polished stem to subsidewithin the cement mantle. The taper of the stem permits it toself-tighten upon the slight movement which occurs during the subsidenceand engage in the hollow centralizer and yet to do so without pullingthe cement mantle and avoiding the disruption of the micro interlockingat the cement bone interface.

This design causes the stem to impart primary compressive forces againstthe cement mantle thus transmitting the load to the femur. Transmittingthe load in this manner forces the cement mantle continuously, snuggly,and firmly against the interior of the femur to assist in maintainingthe integrity of microlocking at the cement bone interface.

Utilizing devices such as those shown in Ling without a collar, however,the surgeon is intra-operatively challenged to position the stems bothaxially and rotationally. The inability to properly position theprosthesis may limit the patient's range of motion by inducing, forexample, improper leg length, inadequate lateral stem offset or noneanatomical version of the stem. Conversely the inclusion of a collar onthe femoral hip joint prosthesis may lessen or eliminate the ability ofthe femoral stem prosthesis to subside and impart the primarycompressive forces against the cement mantle necessary to assure thatthe cement mantle continuously is snugly and firmly against the interiorof the femur to maintain the integrity of the microlocking at the cementbone interface.

The devices as disclosed in the above mentioned Ling patents have beencommercialized in the Zimmer CPT™ tapered highly polished stems. Othersuch stems include the Stryker Howmedica Exeter™ and the C-Stem™ (aDePuy product). These tapered highly polished stems have displayedclinical success, but have done so without the benefits of a collar.Because these designs lack consistent methods of proximal pressurizationand centralization, cement mantle variability has been demonstrated.Meanwhile, collared stems such as the Charnley hip and its derivativeshave also demonstrated excellent results, but do not have the additionaladvantage of controlled long-term subsidence.

Tapered highly polished stems have historically been designed without aproximal collar to prevent cement creep and long term, controlledsubsidence within the cement mantle while simultaneously minimizingcement abrasion. Without the collar, however, the surgeon isintra-operatively challenged to position the stems both axially androtationally. This malposition has been shown to limit the patient'srange of motion by inducing improper leg length, inadequate lateral stemoffset or non-anatomical version of the stem. Inadequate pressurizationof the cement within the femoral canal has also been documented as apotential cause of improper cement technique.

Centralization of the stem within the stem mantle is also critical forsuccess. Non-uniform or excessively thin cement mantles can induce highcement stresses and subsequent cracks that cause failure at thecement-stem-bone interfaces. Cement debris due to abrasions has alsobeen shown to produce excessive third-body of polyethylene acetabularcomponents as well as potentially induce osteolytic reactions and boneresorption that may lead to stem loosening. One single femoral stem thatcan singularly address these clinical issues is the intended solution.

SUMMARY OF THE INVENTION

Accordingly, a need has arisen for a prosthesis, which optimizes cementpressurization while providing for initial and final stem position.

The present invention is a prosthesis with a resorbable collar. Theprosthesis may be a tapered, highly polished femoral prosthesis. Theresorbable collar provides initial rotational and axial positioning. Theresorbable collar also may provide stem centralization andpressurization. The prosthesis, after the collar has been resorbed, willallow for cement creep and controlled, long term subsidence with minimalcement abrasion.

The present invention provides for a prosthesis that includes a collarwhich may be assembled with, for example, a femoral hip stem. The collaris preferably made of resorbable material. The collar provides for amechanical reference for axial and rotational position as well as forpressurization of the cement during insertion. The collar may alsoinclude additional geometry for a proximal centralization of the stemwithin the cement mantle.

A primary purpose of stem collars is proper stem placement with respectto the long bone longitudinal axis. Collars are positioned on theresected end of the long bone and can potentially bear a considerableportion of the patient's weight. Such load carrying of the collar canlead to stress shielding particularly at the proximal medial calcarportion of the resected long bone. The stress shielding leads to boneresorption and bone loss. A resorbable collar may then be used on bothcement and uncemented long bone stems to properly position the stem.After the collar is resorbed, the stress shielding and resultant boneloss otherwise caused by a collar may be reduced.

According to one embodiment of the present invention, there is providedan articulating hemiarthroplasty prosthesis. The prosthesis includes astem for implantation at least partially within the medullary canal of along bone and a collar. The collar is used for positioning duringsurgery the prosthesis within the long bone. The collar is operablyassociated with the stem and extends outwardly therefrom. At least aportion of the collar includes a resorbable material.

According to another embodiment of the present invention there isprovided an articulating hemiarthroplasty prosthesis for use with bonecement. The bone cement forms a bone cement mantle over a portion of theprosthesis. The prosthesis includes a stem for implantation at leastpartially within the medullary canal of a long bone and a collar.

The collar is operably associated with said stem and extends outwardlyfrom the stem. At least a portion of the collar includes a resorbablematerial. The prosthesis also includes a head and a cup. The cup is usedfor engagement with the ball. Prior to the resorbing of the resorbablematerial, the collar is adapted for positioning and supporting theprosthesis within the long bone. Subsequent to the resorbing of theresorbable material, the prosthesis is adapted to provide controlledsubsidence of the stem into the cement mantle of the prosthesis.

According to yet another embodiment of the present invention, there isprovided a hip stem for use in arthroplasty. The hip system includes astem for implantation at least partially within the medullary canal of along bone and a collar. The collar is operably associated with the stemand extends outwardly from the stem. At least a portion of the collarincludes a resorbable material.

According to another embodiment of the present invention, there isprovided a collar for use with a stem for use in arthroplasty. Thecollar is extendable outwardly from the stem. At least a portion of thecollar includes a resorbable material.

According to a further embodiment of the present invention, there isprovided a method for providing total hip arthroplasty. The methodincludes the steps of resecting a long bone, opening a medullary canalof the long bone, inserting cement into the canal, providing a stem,placing a collar in cooperation with the stem, implanting the prosthesisat least partially within the medullary canal, positioning the collar inproximity with the resected portion of the long bone, permitting thecollar to be resorbed, and permitting controlled subsidence of the steminto the cement mantle.

The technical advantages of the present invention include improvedcement pressurization by the utilization of the collar. The presence ofthe collar provides for a sealing interface between the resected boneand the collar. Inadequate pressurization of the cement within thefemoral canal has been documented as a potential cause of impropercement technique.

Further, the presence of the collar provides for improved cement stressdistribution. The presence of the collar improves the ability of thestem to be centralized within the cement mantle. The centralization ofthe stem within the cement mantle improves the uniformity of the cementmantle and reduces the likelihood of thin cement mantles. Thin cementmantles may induce high cement stresses and subsequent cracks that causefailure at the cement-bone-stem interfaces.

Further, the improved pressurization and centralization provided by theresorbable collar serves to reduce cement debris due to abrasion. Cementdebris due to abrasion has been shown to produce excessive third bodywear of polyethylene acetabular components, as well as potentiallyinduce osteolytic reactions and bone resorption that may lead to stemloosening.

Another technical advantage of the present invention is the ability toprovide for an accurate initial and final stem position by utilizing thecollar to position the stem against the resected portion of the bone.This is applicable to both cemented and uncemented stems, as well as tocoated and uncoated stems, including those coated with a porous coatingfor bone ingrowth.

A further technical advantage of the present invention is the ability ofthe resorbed collar to alleviate stress shielding and resultant boneloss particularly to the medial calcar otherwise caused by a traditionalmetal collar.

Other technical advantages of the present invention will be readilyapparent to one skilled in the art from the following figures,descriptions and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and theadvantages thereof, reference is now made to the following descriptiontaken in connection with the accompanying drawings, in which:

FIG. 1 is a plan view of a hip prosthesis implanted into a femur and anacetabulum in accordance with an embodiment of the present invention;

FIG. 2 is a medial end view of a hip stem in accordance with theembodiment of the present invention of FIG. 1;

FIG. 3 is a partial plan view of the hip stem in accordance with theembodiment of the present invention of FIG. 1;

FIG. 4 is view of the hip stem along the line 4-4 in the direction ofthe arrows in accordance with the embodiment of the present invention ofFIG. 1;

FIG. 5 is view of the hip stem along the line 5-5 in the direction ofthe arrows in accordance with the embodiment of the present invention ofFIG. 1;

FIG. 6 is a plan view of a hip stem in accordance with the embodiment ofthe present invention;

FIG. 7 is a medial end view of the hip stem in accordance with theembodiment of the present invention of FIG. 6;

FIG. 8 is a plan view of a resorbable collar of the present inventionfor use in a hip stem in accordance with the embodiment of the presentinvention of FIG. 1;

FIG. 9 is view of the resorbable collar of FIG. 8 along the line 9-9 inthe direction of the arrows;

FIG. 10 is view of the resorbable collar of FIG. 8 along the line 10-10in the direction of the arrows;

FIG. 11 is a plan view of a hip stem shown without the resorbable collarin accordance with a further embodiment of the present invention havinga locking feature to secure the collar to the stem;

FIG. 11A is a partial plan view of a stem of a further embodiment of thepresent invention showing a reverse configuration of the locking featureof FIG. 11;

FIG. 12 is a medial, end view of the hip stem in accordance with theembodiment of the present invention of FIG. 11;

FIG. 12A is a medial, end view of a stem of a further embodiment of thepresent invention showing a groove configuration of the locking featureof FIG. 12;

FIG. 12B is a medial, end view of a stem of a further embodiment of thepresent invention showing a rim configuration of the locking feature ofFIG. 12;

FIG. 13 is a view of the hip stem along the line 13-13 in the directionof the arrows in accordance with the embodiment of the present inventionof FIG. 11;

FIG. 14 is a view of the hip stem along the line 14-14 in the directionof the arrows in accordance with the embodiment of the present inventionof FIG. 11;

FIG. 15 is a plan view of the hip stem of FIG. 11 with the resorbablecollar installed;

FIG. 16 is a medial end view of the hip stem in accordance with theembodiment of the present invention of FIG. 15;

FIG. 17 is a partial plan view of the hip stem in accordance with theembodiment of the present invention of FIG. 15;

FIG. 18 is a view of the hip stem along the line 18-18 in the directionof the arrows in accordance with the embodiment of the present inventionof FIG. 15;

FIG. 18A is a partial auxiliary view of a hip stem in accordance withanother embodiment of the present invention;

FIG. 19 is a view of the hip stem along the line 19-19 in the directionof the arrows in accordance with the embodiment of the present inventionof FIG. 15;

FIG. 20 is a plan view of a resorbable collar of the present inventionfor use in a hip stem in accordance with the embodiment of the presentinvention of FIG. 15;

FIG. 20A is a partial auxiliary view of a resorbable collar inaccordance with another embodiment of the present invention;

FIG. 21 is a view of the resorbable collar of FIG. 20 along the line21-21 in the direction of the arrows;

FIG. 22 is a view of the resorbable collar of FIG. 20 along the line22-22 in the direction of the arrows;

FIG. 23 is a partial plan view of a hip stem with a resorbable collarand no locking feature in accordance with a further embodiment of thepresent invention;

FIG. 24 is a plan view of the hip stem with a resorbable collar inaccordance with a further embodiment of the present invention havinginterlocking neck and stem components with the resorbable collarinstalled;

FIG. 25 is a plan view of the hip stem of FIG. 24 without the resorbablecollar installed;

FIG. 26 is a plan view the neck portion of the hip stem in accordancewith the embodiment of the present invention of FIG. 24;

FIG. 27 is a plan view the body portion of the hip stem in accordancewith the embodiment of the present invention of FIG. 24;

FIG. 28 is a plan view of a resorbable collar of the present inventionfor use in a hip stem in accordance with the embodiment of the presentinvention of FIG. 24;

FIG. 29 is a view of the resorbable collar of FIG. 28 along the line29-29 in the direction of the arrows; and

FIG. 30 is a view of the resorbable collar of FIG. 28 along the line30-30 in the direction of the arrows;

FIG. 31 is a plan view of another embodiment of a hip stem in accordancewith the present invention having a stem with enhanced strength;

FIG. 32 is a plan view of a shoulder prosthesis with a resorbable collarand an interlocking stem and head in accordance with a furtherembodiment of the present invention with the head including a connectionpin;

FIG. 33 is a plan view of a shoulder prosthesis with a resorbable collarand an interlocking stem and head in accordance with a furtherembodiment of the present invention with the stem including a connectionpin;

FIG. 34 is a plan view of a hip prosthesis with a plurality of spacedapart grooves along the prosthesis stem and a resorbable collar whichmay be selectively placed in one of the grooves so that a common stemmay be utilized in patients with varied anatomies in accordance with afurther embodiment of the present invention;

FIG. 35 is a plan view of a hip prosthesis with a resorbable collarincluding an embodiment of a resorbable collar which may be also used asa proximal stem centralizing device which may installed onto the stemalong the neck in accordance with a further embodiment of the presentinvention;

FIG. 36 is a view along the lines 36-36 in the direction of the arrowsof the hip prosthesis of FIG. 35;

FIG. 37 is a top view of a resorbable collar for a hip prosthesisshowing a portion of the hip prosthesis in phantom showing an embodimentof a resorbable collar which may also be used as a proximal stemcentralizing device which may installed into grooves in the stemaccording to a further embodiment of the present invention;

FIG. 38 is a partial cross sectional view along the lines 38-38 in thedirection of the arrows of the hip prosthesis of FIG. 37; and

FIG. 39 is a partial cross sectional view along the lines 39-39 in thedirection of the arrows of the hip prosthesis of FIG. 37.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention and the advantages thereof are bestunderstood by referring to the following descriptions and drawings,wherein like numerals are used for like and corresponding parts of thedrawings. According to the present invention and referring now to FIG.1, an embodiment of the present invention is shown as prosthesis 10. Theprosthesis 10 includes a stem 12. As shown in FIG. 1, the stem 12 issuitable for implantation at least partially within medullary canal 14of long bone 16.

The prosthesis 10 further includes a collar 20 for positioning duringsurgery the prosthesis 10 within the long bone 16. The collar 20 isoperably associated with the stem 12 and extends outwardly in thedirection of arrow 22 from the stem 12. At least a portion of the collar20 includes a resorbable material. Preferably and as is shown in FIG. 1,the collar 20 includes a collar face 24 which is positioned against theresected surface 26 of the long bone 16. The collar 20 thus serves tosupport the prosthesis 10 against the long bone 16 and to provide areference for proper positioning the prosthesis 10 within the medullarycanal 14 over long bone 16.

Preferably and as shown in FIG. 1, the prosthesis 10 preferably furtherincludes a head 30 which is operably associated with the stem 12. Thehead 30 may be operably associated with the stem in any suitable manner.For example, the head 30 may include a cono-frustical recess 32 formingan internal tapered surface 34. As shown in FIG. 1 the stem 12 mayinclude a neck 36 extending proximally in the direction of arrow 40 fromthe collar 20. The neck 36 may include an externally tapered portion 42having an external surface 44. As shown in FIG. 1 the external surface44 of the portion 42 of the neck 36 is matingly fitted to the internalsurface 34 of the head 30.

The prosthesis 10 may further include a cup 46 for pivotal engagementwith the head 30. The cup 46 may be secured to hipbone 50 in anysuitable fashion. For example, the cup 46 may include a hemisphericalouter surface 52 which matingly fits with acetabulum 54 of the hipbone50. The outer surface 52 of the cup 46 may include openings (not shown)to which fasteners (not shown) are fitted for securement to theacetabulum 54 or may include a threaded periphery (not shown) forengagement with the acetabulum 54.

The cup may be in pivotal engagement with the head in any suitablefashion. For example, the head and the cup may have mating surfaces formetal to metal contact with each other or as shown in FIG. 1, a liner 60may be pivotably located between the cup 46 and the head 30. The liner60 may be made of a durable metal or may be made of a non-metalmaterial, for example, a plastic or a ceramic. For example, the liner 60may be made of a high molecular weight polyethylene. For example, theliner 60 may be made of ultrahigh molecular weight polyethylene. Oneparticular ultrahigh molecular weight polyethylene that is well suitedfor this application is sold by DePuy as Marathon® and is generallydescribed in U.S. Pat. Nos. 6,017,975 and 6,228,900 which are herebyincorporated by reference in their entireties.

While the present invention may be practiced with a prosthesis having astem in cementless contact with the long bone 16, preferably, and asshown in FIG. 1, the prosthesis 10 is preferably utilized with bonecement 62 which forms cement mantle 64 over outer periphery 66 of distalportion 70 of body 72 of the stem 12. The cement mantle 64 has athickness T of for example, 0.5 to 4.5 mm.

Preferably, and as shown in FIG. 1, a cavity 74 is formed in themedullary canal 14 of the long bone 16 to permit the prosthesis 10 to beinserted therein. The cavity 74 may be formed by any of various commonlyavailable methods for preparing the long bone 16 for the prosthesis 10for example, the cavity 74 may be formed by reaming or by broaching. Thecavity 74 is formed to sufficient size to provide for the positioning ofthe stem 12 and for the presence of the cement mantle 64 between thestem 12 and cancellous bone 76. The outer hard portion of the long bone16 commonly known as cortical bone 80 is preferably not or minimallyreamed or broached to form the cavity 74.

Preferably and as shown in FIG. 1, portion 82 of the collar 20 extendingoutwardly from the stem 12 in the direction of arrow 22 is preferablyadapted to be resorbed by the body to provide control subsidence of thestem 12 into the cement mantle 64 of the prosthesis 10 after theresorption of the collar. As shown in FIG. 1, resorption of the collar20 will permit the movement of the stem 12 of the prosthesis in thedirection of arrow 84.

It should be appreciated that the invention may be practical without thecement mantle 64. In an application without the use of cement, thecavity 74 is sized to fit the prosthesis 10. An uncemented stem may ormay not include surface coating or treatments including possibly a boneingrowth coating such as Porocoat®, a product manufactured by theassignee of the present invention.

Preferably and as shown in FIG. 1, the body 72 of the stem 12 preferablyhas a shape adapted to provide control subsidence of the stem 12 intothe cement mantle 64 of the prosthesis 10. While a variety of shapes ofthe body 72 of the stem 12 may provide for control subsidence of thestem 12 preferably and as shown in FIGS. 1 and 2 the width of the body72 steadily decreases in the direction arrow 84 along axis 90 of thebody 72.

Referring to FIGS. 1 and 2, not only does the medial lateral width (WML)of the body 72 preferably decrease in the direction of arrow 84, theanterior posterior width (WAP) preferably also decreases in thedirection of arrow 84 along axis 90. The tapering in of the stem 12 inthe direction distally of arrow 84 in combination with the force of loadL in the direction of arrow 91 downwardly, the body 72 of the prosthesisupon resorption of the collar 20 moves or subsides in the direction ofarrow 84 maintaining the pressure on the cement mantle 64. Suchcontinual pressure on the cement mantle serves to promote bone growthand reduce osteolysis.

The stem 12 may be made of any suitable or durable material which isbiocompatible and clinically proven. For example, the stem may be madeof a durable metal for example, a cobalt-chromium-molybdenum alloy, astainless steel alloy or a titanium alloy. Preferably, the outerperiphery 66 preferably has a surface finish which is conducive topermitting cement creep and controlled long-term subsidence. Preferablythus, the outer periphery 66 of the stem 12 should be polished. Forexample, the outer periphery 66 of the stem may have optimally a surfacefinish RA of less than or equal to 15 micro-inches.

The collar 20 may have any suitable shape of its outer peripheryprovided that the collar 20 serves to support the prosthesis 10 along atleast a portion of the resected surface 26 of the long bone 16. Forexample, the collar geometry may take the form of those commonly seen oncurrently marketed prosthesis.

The collar material is preferably made of a resorbable and biocompatiblematerial. Many materials fall into this category and include suchmaterials as PLA (polylactic), PGA (polyglycolide) or vitamin Ederivatives. Vitamin E derivatives are available and are similar tothose materials such as in the DePuy Biostop G product line. The BiostopG material is a mixture of neutral components. These neutral componentsinclude glycerol, gelatin and water. This combination of glycerol,gelatin and water may be totally reabsorbed within 15 days of surgery.

Other materials which may be suitable for the bioresorbable collarinclude monomers and biodegradable polymers.

Monomers include L-lactide, D-lactide, DL-lactide and glycolide.L-lactide is produced by the depolymerization of low molecular weightpoly, made by condensation polymerization of the corresponding L (+)lactic acid.

DL-lactide is produced by the depolymerization of low molecular weightpoly, made by condensation polymerization of the corresponding DL-lacticacid.

D (+) lactide is produced by the depolymerization of low molecularweight poly (D-lactic acid), made by condensation polymerization of thecorresponding D-lactic acid.

Glycolide is produced by the depolymerization of low molecular weightpoly (glycollic acid), made by condensation polymerization of thecorresponding glycollic acid (hydroxyacetic acid).

Polymers include two basic categories known as PLA or polylactide. PLAor polylactide include poly(l)-lactide (poly(d)-lactide, andpoly(dl)-lactide).

Copolymers include poly(l)-lactide-co-d-lactide,poly(l)-lactide-co-dl-lactide and poly(lactide)-co-glycolide.

Bioresorbable materials, when in the form of polymers, resorb throughthe use of two types of biodegradation. The first of this type includesthe rapid loss of polymer mass. This type of degradation, when the rateat which the water penetrates the device exceeds that at which thepolymer is converted into water-soluble materials, (resulting in erosionthroughout the device) is called bulk erosion. All of the commerciallyavailable synthetic devices degrade by bulk erosion.

A second type of biodegradation known as surface erosion, occurs whenthe rate at which the polymer penetrates the device is lower than thatof the rate of conversation of the polymer and to water-solublematerials. Surface erosion results in the device thinning over timewhile maintaining its bulk integrity. Polyanhydrides and polyorthoestersare examples of materials that undergo this type of erosion, when thepolymer is hydrophobic, but the chemical bonds are highly susceptible tohydrolysis. In general, this process is referred to as bioerosion ratherthan biodegradation.

The degradation-absorption mechanism is the result of many inter-relatedfactors, including the stability of the polymer backbone, the presenceof catalyst additives and impurities or plasticizers and the geometry ofthe collar. Preferably, the collar is designed by utilizing materialsand geometry to balance these factors by tailoring a collar to slowlydegrade and transfer stress at the appropriate weight to surroundingtissues as they heal.

Applicants believe that a bioresorbable collar may be designed having aresorption rate varying from as little as a few weeks to as long as oneyear or more. For example, when utilizing vitamin E derivatives such asthat of the Biostop G product, resorption rates of a few weeks wouldoccur. Conversely, when using materials such as PLA and PGA theresorption rates may be respectively as great as 24 months or 6 months.

The physical properties of PLA and PGA may be particularly well suitedfor this application in that PLA has sufficient physical properties tomaintain the loads required in such prosthesis. For example, PLA has atensile strength from 4 to 12,000 psi and PGA has a tensile strength of10,000 psi or greater.

Preferably, the bioresorbable polymers for use as materials for thecollar of the present invention are thermoplastic. These thermoplasticmaterials can be processed into different product shapes usingconventional plastic processing techniques for example, extrusion andinjection molding. The process and conditions depend on the particularpolymer and inherent viscosity. It is recommended that the polymers bethoroughly dried before malprocessing using suitable drying conditions.

The bioresorbable materials for use in the collar are preferablysterilized. The most commonly used sterilizing methods for suchpolymers, for example, lactide/glycolide type polymers are gassterilization (ethylene oxide, ETO) and gamma sterilization. ETOsterilization does not substantially effect the molecular properties ofthese polymers. Care must be taken that gas residues are sufficientlyremoved from the material. Gamma radiation is known to result in asignificant decrease in the molecular weight of these polymers. Thiseffect should be taken in account during the development phase of thecollar.

Due to the biodegradable nature of the polymers for use as materials forthe bioresorbable collar (storage conditions below 0° centigrade/32°Fahrenheit should be maintained, preferably at −15° centigrade or 5°Fahrenheit or at a lower temperature. The cold storage serves as anadditional precaution against hydrolysis loss. Before use, the packageshould be allowed to reach room temperature to avoid condensation ofatmospheric moisture. When opened, the material should be used asquickly as possible and be sealed, after purging with high purity drynitrogen, in order to keep out atmospheric moisture.

Preferably, since the resorbable material in the collar is biodegradableand thus affected by the atmospheric conditions, the length of storageof the bioresorbable collar and the conditions, including temperatureand atmosphere in which the bioresorbable collar is stored, should becarefully controlled. The metal stem and other components of theprosthesis of the present invention do not require the same precautionsfor degradation of the material as the bioresorbable collar. Thus, andas shown in the drawings, the bioresorbable collar is designed to beinstalled into the prosthesis near the location in which the orthopaedicsurgery is to be performed, for example, in or near the operating room.

For example, the collar may be inserted onto the stem or assembledthereto by either advancing the collar radially inward toward the stemor advancing the collar axially in a distal direction toward theindentation of the stem.

An example of the prosthesis according to the present invention wherethe collar is inserted onto the stem by advancing the collar radiallyinward toward the stem is shown in FIGS. 1-10. Referring now to FIGS. 2and 3, the stem 12 may include an indentation or groove 92 positionedbetween the body 72 of the stem 12 and the neck 36. The indentation orgroove 92 is preferably positioned such that face 24 of the collar 20when inserted into the groove 92 is positioned along the resection line26.

While the indentation 92 may have any suitable form, preferably theindentation 92 is in the form of a groove. The groove 92 preferably hasa width TG which corresponds with the thickness TC of the collar 20. Thecollar 20 is insertable onto the stem 12 by advancing the collar 20 inthe direction of arrow 94. The respective width TC and TG of the collarand groove respectively are sized for proper securing of the collar 20and may, for example, provide for a sliding fit of the collar 20 or fora slight interference fit therewith.

It should be appreciated that by providing the insertable collar 20, thestem 12 and the collar 20 may be separately packaged such that thestorage requirements of the stem 12 and the storage shelf liferequirements of the collar may be optimized.

Referring now to FIG. 4, the stem 12 is shown in an anterior/posteriorview with the groove 92 located on the stem 12. The groove 92 includesinner faces 96 to which the collar 20 may be matingly fitted.

Referring now to FIG. 5, a view of the hip stem 12 is shown along theline 5-5 in the direction of arrows in accordance with the embodiment ofthe present invention of FIG. 1. The anterior/posterior boundaries 96and medial/lateral boundaries 100 of the groove 92 are shown as hiddenlines.

Referring now to FIGS. 1, 6 and 7, an anterior/posterior view and amedial/lateral view of the prosthesis 10 including the stem 12 and thecollar 20 are shown.

Referring now to FIG. 8, a plan view of the resorbable collar 20 of thepresent invention for use in the hip stem 12 in accordance with theembodiment of the present invention of FIG. 1 is shown. The collar 12includes an arcuate medial portion 110 and a pair of arms 112 extendingtherefrom. The arms 112 are separated by a distance WIC corresponding tothe WIG between inner faces 96 of the groove 92 (see FIG. 4).

Referring now to FIGS. 9 and 10, the collar 20 may, as shown, be planerand having a thickness (TC) corresponding to the thickness (TG) of thegroove 92 (see FIG. 3).

Referring now to FIGS. 11 through 22 another embodiment of the presentinvention is shown as prosthesis 210. With prosthesis 210, the collar isinserted onto the stem by advancing the collar axially in a distaldirection toward the indentation of the stem.

Referring now to FIG. 11, prosthesis 210 is similar to prosthesis 10 ofFIG. 1 except that prosthesis 210 includes a locking feature 218 in stem212 which mates with a locking feature 228 in collar 220 (see FIG. 18).The locking feature as shown in FIG. 11 is preferably on the medial sidewhere loads on the collar will be the greatest. It should be appreciatedthat the locking feature may be positioned on the lateral side, theanterior side, or the posterior side or any combination thereof.

The stem 212 is similar to stem 12 and is made of a similar suitabledurable material. The stem 212 includes a body 272 and a neck 236. Theneck 236 extends from the body 272 at resection surface 226.

Preferably and as shown in FIG. 11, the locking feature 218 of the stem212 of the prosthesis 210 is preferably positioned on outer periphery239 of the neck 236 near the resection surface 226.

The locking feature 218 may be in any suitable form to provide for alocking feature between the stem 212 and the collar 220 (see FIG. 15).For example, and as shown in FIG. 11, the locking feature 218 of thestem 212 may be in the form of a dimple 218. The dimple 218 may be, forexample, a generally hemispherical cavity or depression on the periphery239 of the neck 236 of the stem 212. While in FIG. 11 a solitary dimple218 is shown, it should be appreciated that a plurality of dimples maybe preferred.

Referring now to FIG. 12, the stem 212 of the prosthesis 210 is shown inthe posterior/anterior plane. The neck 236 of the body 272 shows aplurality of dimples 218 thereon.

Referring now to FIG. 13, the neck 236 of the stem 212 is shown ingreater detail. The neck 236 includes opposed dimples 218 located onouter periphery 239 of the neck 236.

Referring now to FIGS. 14 and 15, a resorbable collar 220 according tothe present invention is located positioned on the stem 212. The collar220 is installed by advancing it distally in the direction of arrow 219against resection surface 226 of the body 272 of the stem 212.

Referring now to FIG. 16, the collar 220 as shown installed onto thestem 212. The collar 220 is located between body 272 and the neck 236.At least a portion of the collar 220 extends out beyond the body 272 andprovides a support for the stem 212 when installed against a resectedlong bone (not shown).

Referring now to FIG. 14, the collar is shown enlarged and positionedbetween the neck 236 and the body 272.

Referring now FIGS. 18 and 19, the locating feature for use with theprosthesis of the present invention including the resorbable collar isshown in prosthesis 210 as dimple 218 on stem 212 which mates with bump228 on the collar 220. The collar 220 is positioned between the body 272and the neck 236. As shown in FIG. 18, the prosthesis 210 may include apair of opposed bumps 228 which mate with a pair of opposed dimples 218on the stem 212.

Referring now to FIGS. 20, 21 and 22, the collar 220 for use with thestem 212 to provide prosthesis 210 of FIG. 18 according to the presentinvention is shown. The collar 220 includes an internal opening 249 topermit the collar 220 to fit against outer periphery 239 of the neck 236of the stem 212 (see FIG. 13). The collar 220 includes locking featuresin the form of bumps extending inwardly from the collar 220 at theperiphery of the hole 249. As shown in FIG. 20, four diametricallyopposed bumps 228 are located on the collar 220.

Referring now to FIGS. 11A, 18A and 20A, an alternate embodiment of thepresent invention is shown as prosthesis 310 including stem 312. Theprosthesis 310 includes an alternate configuration for the lockingfeature. This alternate configuration is in the form of a bump 328formed on outer periphery 339 of neck 336 of the prosthesis 310.

Referring now to FIG. 18A the stem 312 of the prosthesis 310 includesthe bump 328 which mates with dimple 318 located on collar 320.

Referring now to FIG. 20A the dimple 318 extends outwardly from the hole349 on the collar 320.

Referring now to FIG. 12A, an alternate embodiment of the presentinvention is shown as prosthesis 410 including stem 412 having a lockingfeature in another form. For example, as shown in FIG. 12A, the lockingfeature is in the form of a groove 418 located on the outer periphery439 of the neck 436 of the stem 412 of the prosthesis 410. It should beappreciated that the groove 418 of the stem 412 of the prosthesis 410may be utilized in connection with either bumps or an internal rimextending from the hole of the collar (not shown).

Referring now to FIG. 12B, an alternate embodiment of the presentinvention is shown as prosthesis 510 including stem 512 having a lockingfeature in another form. The locking feature of FIG. 12B for use withthe resorbable collar prosthesis of the present invention is in the formof a rim 518. The rim 518 extends outwardly from external periphery 539of neck 536 of the stem 512 of the prosthesis 510. The rim 518 maycooperate with an internal groove located on the hole of the collar (notshown) or merely provided interference fit with the hole of the collar.

Referring now FIG. 23 another embodiment of the present invention isshown as prosthesis 610. Prosthesis 610 is similar to prosthesis 210except that the prosthesis does not include a locking feature. Theprosthesis 610 includes a stem 612 similar to stem 212 of the prosthesis210 and includes a body 672 similar to body 272 of the prosthesis 210and a neck 636 similar to neck 236 of the prosthesis 210. In addition tothe stem 612 the prosthesis 610 includes a collar 620 which mates withthe stem 612 to form the prosthesis 610. The collar 620 is similar tothe collar 220 of the prosthesis 210 but does not include a lockingfeature. The stem 612 and the collar 220 are interconnected by aninterference fit.

Referring now to FIGS. 24 through 30, prosthesis 710 according to thepresent invention is shown. The prosthesis 710 includes a stem 712 whichhas a body 772 and a neck 736. The neck 736 is removably connected tothe body 772. Therefore, the stem 712 includes a body component 768 anda neck component 758. The prosthesis 710 also includes a collar 720which restrainably positional between the body 772 and the neck 736.

The prosthesis according to the present invention may include a neckcomponent 758 which is removably connected to a body component 768 inany suitable fashion. For example, the body component 768 and the neckcomponent 758 may be connected by threadable connection, by bayonetconnection or twist locking connection.

As shown in FIG. 24, the prosthesis 710 may include a tapered maleconnector 738 in the neck component 758 which mates with a taperedfemale connection 748 located in the body component 768. It should beappreciated, however, that the tapered male connector 738 may, as well,be located in the body component 768 and the tapered female connector748 may as likewise be located in the neck component 758.

The body component 768 includes a body 772 similar to the body 272 ofthe prosthesis 210 while the neck component 758 includes a neck 736which is similar to the neck 236 of the prosthesis 210. The neckcomponent 758 and the body component 768 are made of a material similarto the stem 12 of FIG. 1.

Referring now to FIG. 25, the prosthesis 710 is shown without the collar720 in place. The body component 768 is shown in connection with theneck component 758. A gap or space 789 is shown between the paralleladjoining surfaces of the outer periphery of the neck component 758 anda body component 768. It is in this gap 789 that the collar 720 may befitted. The tapered male connector 738 and the tapered female connector748 are sized such that the gap 789 between the neck 736 and the body772 is selected to provide for a secure positioning of the collar 720.

Referring now FIGS. 26 and 27, the neck component 758 and the bodycomponent 768 are shown as separate components. The neck component 758includes the neck 736 to which the tapered male connector 738 isconnected. The body component 768 includes the body 772 in which thetapered female connector 748 is formed.

Referring now to FIGS. 28 through 30, the collar 720 is shown. Thecollar 720 is similar to collar 20 of the prosthesis 10 and ispreferably made of a resorbable material. Appropriate resorbablematerials have been described herein. The collar 720 includes a hole 758for permitting the tapered male connector 738 and the tapered femaleconnector 748 to interconnect therebetween (see FIG. 25).

Referring now to FIG. 31 a partial view of another embodiment of thepresent invention utilizing the resorbable collar is shown as prosthesis810 having stem 812. The stem 812 is shown with a shape to improve thestrength/weight ratio of the stem. As shown in FIG. 31, body 872 of thestem 812 is similar to the body 72 of the stem 12 of FIG. 1, butincludes a step 802 running vertically along the stem 872. The step 802provides for extra strength for the stem 812.

The body 872 as shown in FIG. 31 further includes an external stemrecess 804 running vertically along distal portion 870 of the body 872of the stem 812. The stem recess 804 provides for additional stiffnessof the stem 812. The body 872 may further include a manufacturingreference hole 806 for use in fixturing the stem 812 duringmanufacturing. A collar 820 is spaced between body 872 and neck 836.

Referring now to FIG. 32 a plan view of another embodiment of thepresent invention utilizing the resorbable collar is shown as shoulderprosthesis 910. Shoulder prosthesis 910 includes a stem 912 having atapered cavity 948 and a resorbable collar 920. The shoulder prosthesis910 also includes a head 930 having a connection pin 938. The connectionpin 938 in the head 930 interlocks with the tapered cavity 948 of thestem 912. The resorbable collar 920 is sandwiched between the stem 912and the collar 920.

Referring now to FIG. 33 a plan view of another embodiment of thepresent invention utilizing the resorbable collar is shown as shoulderprosthesis 1010. Shoulder prosthesis 1010 includes a stem 1012 having aconnection pin 1038 and a resorbable collar 1020. The shoulderprosthesis 1010 also includes a head 1030 having tapered cavity 1048.The connection pin 1038 in the stem 1012 interlocks with the taperedcavity 1048 of the head 1030. The resorbable collar 1020 is sandwichedbetween the stem 1012 and the collar 1020.

It should be appreciated that the stem or collar of the prosthesis ofthe present invention may be adapted to provide for a selectableplurality of implantable positions of the collar with respect to thestem. For example, and referring now to FIG. 34, a prosthesis 1110 isshown which provides for a plurality of selectable implantable positionsfor the collar with respect to the stem.

The prosthesis 1110 is similar to prosthesis 10 of FIG. 1 and includes astem 1112 which is generally similar to stem 12 of prosthesis 10 ofFIG. 1. The prosthesis 1110 further includes a head 1130 which isfittable to stem 1112. The head 1130 is similar to head 30 of prosthesis10 of FIG. 1. The prosthesis 1110 further includes a cup 1146 which isfitted to acetabulum 54. The cup 1146 is similar to cup 46 of theprosthesis 10 of FIG. 1 and may, as the prosthesis 10 of FIG. 1, includea liner 1160 similar to liner 60 of the prosthesis 10 of FIG. 1.

As shown in FIG. 34, the stem 1112 may include grooves 1192 with each ofthe grooves 1192 being similar to groove 92 of the stem 12 (see FIG. 3).

As shown in FIG. 34, the prosthesis 1110 may include among the grooves1192 a first groove 1111 which is shown in position against resectedsurface 26 of the long bone 16. As shown in FIG. 34, the first groove1111 is shown generally perpendicular to medial surface 1113 of the stem1112. The collar 1120 preferably matingly fits within the first groove1110 to provide support for the stem 1112 in accordance to the presentinvention.

In addition to the first groove 1111, the stem 1112 may include a secondgroove 1115 which is spaced from first groove 1111. The second groove1115 is similar in size and configuration with the first groove 1111.The second groove 1115 may be parallel to the first groove 1111 or may,like first groove 1111, be generally perpendicular to medial surface1113 of the stem 1112.

In addition to the first groove 1111 and the second groove 1115, theprosthesis 1110 may include a third groove 1117 positioned on stem 1112.The third groove 1117 may be parallel and spaced from first groove 1111and second groove 1115 or may be perpendicular to the medial surface1113 of the stem 1112. Similar to the first groove 1111 and the secondgroove 1115, the third groove 1117 is provided with the size and shapefor secure cooperation with the collar 1120.

As shown in FIG. 34, when the collar 1120 is in first groove 1111, thecollar 1120 is in a first collar position 1121. At first collar position1121, the head 1130 is in first head position 1131 as shown in solid.Similarly, when the collar 1120 is in second groove 1115 as shown inphantom, the collar 1120 is in second collar position 1123 andcorrespondingly the head 1130 is in second head position 1133 as thestem 1112 is moved in the direction of arrow 1141 to provide for thecollar 1120 to rest against resected surface 26 when the collar 1120 isin the second groove 1115.

Similarly, when the collar 1120 is positioned in third groove 1117, thecollar is in third collar position 1125, as shown in phantom, and thestem, after moving in the direction of arrow 1141, results in the head1130 being in third head position 1135 as shown in phantom. Thus, it canbe shown that by utilizing the prosthesis 1110, a common stem 1112 andcollar 1120 may be utilized to provide for a variety of head positionsutilizing the same prosthesis 1110. Thus, the prosthesis 1110 may beutilized for patients with a variety of anatomical needs.

Referring now to FIGS. 35 and 36, another embodiment of the presentinvention is shown as prosthesis 1210. Prosthesis 1210 provides anadditional advantage of providing for proximal centralization of theprosthesis within the broached cavity of the medullary canal.Centralization of the prosthesis 1210 within the broached cavityprovides for uniform cement mantle around the prosthesis which providesfor optimum support for the prosthesis within the patient.

The prosthesis 1210, as shown in FIGS. 35 and 36, is similar to theprosthesis 210 of FIGS. 11 to 20. The prosthesis 1210 includes a stem1212 to which a head 1230 is attached. The head 1230 rotates about cup1246 secured to acetabulum 54. As shown in FIGS. 35 and 36, theprosthesis 1210 may include a liner 1260 positioned between the cup 1246and the head 1230. The head 1230, the cup 1246, and the liner 1260 ofthe prosthesis 1210 may be similar to the head 230, the cup 246 and theliner 260 of the prosthesis 210 of FIGS. 11 to 20.

The stem 1212 of the prosthesis 1210 is similar to the stem 212 of theprosthesis 210 of FIGS. 11 to 20 and includes a dimple 1218 forreceiving collar 1220. The collar 1220 includes a bump 1228 which mateswith the dimple 1218 of the neck 1236 of the stem 1212. The dimple 1218and the bump 1228 serve to provide support for the stem 1212 duringinstallation of the stem 1212 into the cavity 74 formed in medullarycanal 14 of the patient.

The collar 1220 is somewhat different than collar 220 of the prosthesis210 of FIGS. 11 to 20 in that the collar 1220 further serves tocentralize the stem 1212 within the cavity 74. In order that the collar1220 may be utilized to centralize the stem 1212, the collar 1220includes a collar outer periphery 1281 which is designed to matingly fitwith cavity periphery 1283. A portion of collar 1220 may rest onresected surface 26 of the long bone 16. The collar 1220 may rest on thecancellous bone 76 or may also rest on cortical bone 80. To provide acentralizing feature in the collar 1220 adjacent the portion of thecollar 1220 that rests upon resected surface 26, the collar 1220 mayinclude a lip 1285 which forms a collar inner-periphery 1287. The collarinner-periphery 1287 matingly fits with cavity periphery 1283 to assistin centralizing the collar 1220.

By placing the collar 1220 onto neck 1236 of the stem 1212, the collar1220 centralizes the stem 1212 within cavity 74. The stem 1212 thus isan equal distance preferably of TT from cavity periphery 1283 formed bycavity 74. The space between the cavity periphery 1283 and the stem 1212is filled with PMMA and forms cement mantle 1264 between the cancellousbone 76 and the stem 1212. The thickness of the cement mantle 1264 thusis uniformly a thickness of TT. By providing a uniform thickness of thecement mantle 1264, the implantation of the prosthesis 1210 may beoptimized.

Referring now to FIGS. 37, 38 and 39, another embodiment of the presentinvention is shown as prosthesis 1310. Prosthesis 1310, like prosthesis1210 of FIGS. 35 and 36, provides for proximal centralization of thestem by utilizing a centralizing collar. The prosthesis 1310 is similarto prosthesis 10 of FIGS. 1 through 10 and includes a stem 1310 (shownin phantom) similar to stem 12 of FIGS. 1 through 10.

The prosthesis 1310 further includes a collar 1320 similar to collar 20of FIGS. 1 through 10 except that the collar 1320 has been adapted tocentralize the stem 1312 within the cavity 74 of the prosthesis 1310.The collar 1320 thus includes a collar outer-periphery 1381 whichcontacts cavity periphery 1383 formed by cavity 74 in the cancellousbone 76 of the long bone 16.

The prosthesis 1310 may further include a lip 1385 which providessupport for the prosthesis 1310 by having the lip 1385 rest againstresected surface 26 of the cancellous bone 76. The lip 1385 forms collarinner-periphery 1387. The collar inner-periphery 1387 furthercentralizes the collar 1320 within the cavity 74. It should beappreciated that the collar outer-periphery 1381 and the collarinner-periphery 1387 may generally correspond in shape to the cavity 74or the stem 1312 or may, as shown in FIGS. 37, 38 and 39, includearcuate protrusions 1391. The arcuate protrusions 1391 may be used tocontact the cavity periphery 1383 of the cavity 74.

By providing a highly polished tapered femoral prosthesis that isassembled with a collar made of a resorbable material, a process may beprovided that utilizes a collar to improve cement pressurization.

By providing a highly polished tapered female prosthesis that isassembled with a resorbable collar the cement stress distribution may beoptimized by providing for a proper positioning of the prosthesis and bypermitting control subsidence of the prosthesis.

By providing a highly polished tapered femoral prosthesis with aresorbable collar a consistent cement mantle thickness may be providedby utilizing the collar to properly position the prosthesis.

By providing a highly polished tapered femoral prosthesis with aresorbable collar, the generation of cement debris may be minimized. Byproviding a highly polished tapered femoral prosthesis with a resorbablecollar, initial and final stem position may be optimized by utilizingthe collar to properly position the prosthesis against the resectionline of the femur.

It should be appreciated that while the figures of the present inventionshow the use of a prosthesis with a resorbable collar in the form of afemur hip stem, it should be appreciated that the invention may beequally suitable for a shoulder prosthesis. A resorbable collar may bedesirable to position a shoulder stem into the humerus and to locate theshoulder against the resected humerus.

It should also be appreciated that a resorbable collar may be desirablein other long bones for example, in an ulna or a tibia.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions, andalterations can be made therein without departing from the spirit andscope of the present invention as defined by the appended claims.

1. An articulating hemiarthroplasty prosthesis comprising: a stem forimplantation at least partially within the medullary canal of a longbone, and a collar for positioning during surgery the prosthesis withinthe long bone, said collar being operably associated with said stem andextending outwardly therefrom, at least a portion of said collarcomprising a resorbable material.
 2. The prosthesis of claim 1: whereinthe prosthesis comprises an articulating hemiarthroplasty prosthesis,further comprising a head operably associated with said stem, andfurther comprising a cup for pivotable engagement with said head.
 3. Theprosthesis of claim 2, wherein said stem and said head are integral witheach other.
 4. The prosthesis of claim 1 for use with bone cement, thebone cement forming a bone cement mantle over a portion of said stem:wherein the portion of said collar extending outwardly from said stem isadapted to be resorbed by the body to provide controlled subsidence ofsaid stem into the cement mantle of the prosthesis after the resorptionof the collar; and wherein said stem comprises a shape adapted toprovide controlled subsidence of said stem into the cement mantle of theprosthesis.
 5. The prosthesis of claim 1: wherein an outer periphery ofsaid stem defines an indentation therein; and wherein said collarincludes an outer surface thereof adapted to mate with the indentation.6. The prosthesis of claim 5, wherein said collar is inserted onto saidstem by at least one of advancing said collar radially inwardly towardsaid stem and advancing said collar axially in a distal direction towardthe indentation of said stem.
 7. (canceled)
 8. The prosthesis of claim1, wherein said resorbable material comprises at least one of apolylactide, a polyglyolide, a vitamin E derivative, a glycerol, agelatin and a polymer or a co-polymer.
 9. The prosthesis of claim 1,wherein at least one of said stem and said collar are adapted to providefor one of a selectable plurality of implantable positions of saidcollar with respect to said stem.
 10. The prosthesis of claim 1, whereinsaid collar is adapted to centralize said stem within the medullarycanal.
 11. The prosthesis of claim 1, wherein said stem is adapted foruse with bone cement.
 12. An articulating hemiarthroplasty prosthesisfor use with bone cement, the bone cement forming a bone cement mantleover a portion of the prosthesis, said prosthesis comprising: a stem forimplantation at least partially within the medullary canal of a longbone, a collar operably associated with said stem and extendingoutwardly therefrom, at least a portion of said collar comprising aresorbable material, and a head, and a cup for engagement with saidball, wherein prior to the resorbing of the resorbable material, saidcollar being adapted for positioning and supporting the prosthesiswithin the long bone and wherein subsequent to the resorbing of theresorbable material said prosthesis being adapted to provide controlledsubsidence of said stem into the cement mantle of the prosthesis. 13.The prosthesis of claim 12: wherein an outer periphery of said stemdefines an indentation therein; and Wherein said collar includes anouter surface thereof adapted to mate with the indentation. 14.(canceled)
 15. The prosthesis of claim 12, wherein said resorbablematerial comprises at least one of polylactide, a polyglyolide, avitamin E derivative, a glycerol, a gelatin and a polymer or aco-polymer.
 16. The prosthesis of claim 12, wherein at least one of saidstem and said collar are adapted to provide for one of a selectableplurality of implantable positions of said collar with respect to saidstem.
 17. The prosthesis of claim 12, wherein said collar is adapted tocentralize said stem within the medullary canal.
 18. The prosthesis ofclaim 12, wherein said stem is adapted for use with bone cement.
 19. Ahip stem for use in arthroplasty comprising: a stem for implantation atleast partially within the medullary canal of a long bone; and a collaroperably associated with said stem and extending outwardly therefrom, atleast a portion of said collar comprising a resorbable material.
 20. Thehip stem of claim 19: wherein an outer periphery of said stem defines anindentation therein; and wherein said collar includes an outer surfacethereof adapted to mate with the indentation.
 21. The hip stem of claim19 adapted for use with bone cement, the bone cement forming a bonecement mantle over a portion of said stem.
 22. The hip stem of claim 21,wherein said stem is adapted to provide controlled subsidence of saidstem into the cement mantle of the prosthesis after the resorption ofthe collar.
 23. The hip stem of claim 19, wherein said resorbablematerial comprises at least one of a polylactide, a polyglyolide, avitamin E derivative, a glycerol, a gelatin and a polymer or aco-polymer.
 24. The hip stem of claim 19, wherein at least one of saidstem and said collar are adapted to provide for one of a selectableplurality of implantable positions of said collar with respect to saidstem.
 25. A collar for use with a stem for use in arthroplasty, thecollar being extendable outwardly from the stem, at least a portion ofsaid collar comprising a resorbable material.
 26. The collar of claim 25for use with a stem and with bone cement, the bone cement forming a bonecement mantle over a portion of the stem, said collar being adapted forpositioning and supporting the prosthesis within the long bone andwherein subsequent to the resorbing of the resorbable material saidprosthesis being adapted to provide controlled subsidence of said steminto the cement mantle of the prosthesis.
 27. The collar of claim 25,wherein said resorbable material comprises at least one of polylactide,a polyglyolide, a vitamin E derivative, a glycerol, a gelatin and apolymer or a co-polymer.
 28. The collar of claim 25, wherein said collaris adapted to centralize said stem.
 29. (canceled)
 30. (canceled) 31.(canceled)